DISEASES TRANSMISSIBLE FROM MONKEYS TO MAN

Ron Hines, DVM PhD

Before reading this article, Please read my disclaimer.

I have cared for monkeys for most of my career. I have also owned quite a few. But if you do not already have a pet monkey, think long and hard before you decide to get one. Monkeys are an enormous challenge. It is extremely difficult to establish a stable, non-institutional environment where both the monkey and the owner remain happy and healthy. In most cases, a time will come when the monkey, the owner, a family member or a neighbor will be injured or harmed. Usually, these are physical situations where a frustrated monkey attacks people. But the damage can also be due to illness spread by the monkey.

There was a time when the majority of monkeys available in the United States were wild animals that had been trapped in tropical areas around the World. They came from many different locations and Continents and brought with them a host of diseases. Some of these diseases, they naturally carried, others they caught from the natives and jobbers who trapped them.

Disease organisms, particularly virus, tend to live only in a small group of animal species to which they have adapted. In those species, the virus often does little or no damage. That is why exotic pets other than monkeys are much less likely to make their owners ill. But humans are primates of a sort - similar to monkeys - and many of the disease causing organisms that belong in sub-human primates, can live in humans and go out of control. When they do, they can cause a much more severe disease than in the monkeys in which they belong.

The monkeys of Central and South America (New World monkeys) have been isolated from those of Africa and Asia (Old World monkeys) for 40 million years. In that time, New World monkeys they have become distinctive. The easiest way to recognize New World monkeys is that almost all of them have prehensile (grasping tails). Another key difference is their resistance to many diseases that affect Old World monkeys. It is the Old World monkeys that carry most of the diseases that are dangerous to humans. Even the tuberculosis organism obeys that rule – New World monkeys are more resistant to tuberculosis while Old World Monkeys are highly susceptible to it.

In October 1975, the U.S. Public Health Service banned the importation of all monkeys to be sold as pets, restricting imports only those “essential for scientific and exhibition use”. This law (42 CFR 71.53(c)) further states the "maintenance of nonhuman primates as pets, hobby, or an avocation with occasional display to others is not a permissible use”. The law, however, is unclear as to which monkeys it is referring to so pet monkeys are still readily available.

This article discusses some of the diseases we currently know of that wild monkeys sometimes carry and that are a threat to human health. Many of these diseases are less likely to exist in captive bred, disease monitored, monkeys than they are ,or were, in wild-caught, imported monkeys. Some are also quite unlikely to occur in New World Monkeys. With the recent advent of very accurate PCR tests for monkeys, breeders and prospective purchasers of monkeys have a way to be certain the animal does not harbor any of these diseases.

There are other dangerous diseases that monkeys transmit to people in their homelands. Those diseases, like Yellow Fever, falciparum malaria , Kyasanur Forest disease, Tanapox and Mayaro virus depend on mosquitoes, ticks and biting flies to transmit from monkeys to humans. Others, like leprosy, have never been reported to have transmitted from infected monkeys to humans. Pet monkeys in the United States are not a source of these diseases, so I do not cover them. Diseases like Monkey Pox are misnamed and have little to do with monkeys. Although Simian virus 40 is present in many monkeys, most people are exposed to it through vaccines containing monkey tissue – not contact with monkeys.

How Are Most People Exposed To Monkey Diseases?

Diseases of animals that also infect humans are called zoonoses. Most of these diseases are spread through a bite or exposure to the saliva of monkeys or their nasal secretions. The rest are spread through exposure to monkey feces.

Monkeys are subject to sudden and violent mood swings – particularly those with identity issues resulting from having been bottle-fed as surrogate human infants.

A monkey that is peacefully grooming or playing can, without warning, attack strangers or family members it finds threatening or as rivals for attention and affection. Monkeys also have a strict peck order. Sometimes their attacks are attempts to assert themselves in their perceived peck order. Fearful monkeys also bite to defend themselves. Most people who casually encounter a pet monkey are unaware how quickly its mood can change. There are just not that many pet monkeys around, so people judge their personalities and threat based on their experience with imaginary, good-natured cartoon monkeys, circus acts and books like Curious George.

Most monkey owners treat their pets as family members. Monkeys are very unsanitary creatures – whatever disease organisms they harbor in their intestines and blood, will soon be shared with every member of the family.

If I Have Been Exposed To A Monkey Through A Bite Or Close Contact, What Should I Do?

If this was an isolated, US-born, healthy, pet monkey and it is known to be tuberculosis and herpes-B negative, you are probably not at any significant risk. I have been bitten and exposed to hundreds of monkeys and have never become ill.

If you were bitten, you need to consider if you want to inform local officials. Most officials pass the buck on what to do back to their local Health Department. And most Health Departments are not sympathetic to pet monkeys. Many will insist the monkey be killed and its head sent off for rabies testing. This is unfortunate, because monkeys are not a significant source of rabies. The only US case I know of occurred in 1911 and that monkey was bitten by a rabid dog. But that’s the way the law works. So you must decide if you want to be responsible for this to happen.

What you should most certainly do if you have been bitten or scratched, is to scrub the wound immediately with antiseptic Betadine (povone iodine) Or Septisol/Phisohexx (hexachlorphene cleanser) and rinse, and then flush the wound liberally with warm water. How long? The Canadians suggest the longest - 15-20 minutes.

If you are concerned, if the monkey's health is in doubt, if the wound is major, if it becomes infected or if your feel ill, go see your doctor. Your General Practitioner will not know what to do either – how often does he/she see monkey bites? Have them call ZVED for advice (National Center for Zoonotic, Vector-Borne, and Enteric Diseases).

If this was a bite, wound, scratch or exposure of your lips, mouth, nose or eyes to the saliva, sneeze or cough of a rhesus monkey or another macaque monkey or a puncture from an instrument that was in contact with any of those species and the Herpes-B and tuberculosis status of the animal is unknown, uncertain or positive, have your physician call ZVED (800-232-4636).

Can Monkeys Catch Illnesses From You Or Your Other Pets ?

Yes. Pet monkeys catch many more illnesses from people than they transmit to people.

Colds

My capuchin colony monkeys often developed sneezing and upper respiratory inflammation very similar to be the colds that their keepers were experiencing. I do not know of any scientific studies that have been done to characterize these infections in monkeys but I assume they occur.

Measles

A common problem in monkeys is human measles (rubeola, not rubella) Since most people in the US are now vaccinated against measles, it is much less common in pet monkeys than it once was. New World monkeys are more resistant to it than Old World monkeys, but it can be fatal to both. The signs of measles in monkeys is rash, fever, facial swelling and eye and nasal discharges. The incubation period after being exposed to a human with measles is 9-11 days. Moneys can be vaccinated against measles with the human vaccine (Attenuvax) after they are six months old. A titre of 1:4 protects them. Institutions also give their monkeys the M-M-R II vaccine. This protects against mumps and rubella as well as measles. If the monkey is less than 1 month old, a second shot is given at 15 month. Some zoos give a booster vaccination when the monkey is 10-12 years old.

Polio

Poliomyelitis can occur in chimps and other great apes, colobus monkeys and possibly other monkey species as well. When it affects monkeys, polio virus can produced the same disease it does in man. Monkeys can be immunized with the same oral vaccines we give to children.

Rabies

I do not personally know of reported cases of rabies in primates. Some references say that approximately 11 cases have occurred in monkeys in US history. No anti-rabies vaccine is approved for use in monkeys. Zoos do not vaccinate their monkeys against rabies. However, there might be instances when a pet monkey bites a human where local health department authorities might allow a rabies quarantine rather than immediately killing the monkey to have it examined for rabies if it were vaccinated. These decisions are generally made locally in the City where you live. So pet monkey owners might consider having their pets vaccinated against rabies. If done, the human Imovax or Merck Imrab vaccine would be used. These are not approved uses for these vaccines and in no way force public health officials to spare the monkey’s life.

Tetanus

Monkeys, like humans catch tetanus from contaminated wounds. Monkeys should be vaccinated against tetanus. They need to receive the two vaccinations at 4- 5 week intervals and a booster 12 months later. Revaccinate them every 5-6 years.

Tuberculosis

Old World monkeys are very susceptible to human and cattle tuberculosis. Unlike humans, moneys have no natural resistance to the disease. When they do catch it from a human, it usually spreads very fast in their bodies and to areas other than their lungs. So unlike in humans, tuberculosis in monkeys is usually a rapid, severe and fatal disease. During their illness, they can spread the disease to anyone who comes in contact with them or their waste. More information on tuberculosis in monkeys is given farther down in this article.

Because of this threat, all monkeys should have a TB test at least annually.

Why Are Monkey Diseases So Serious When They Affect Humans?

I mentioned earlier that many virus diseases that cause only minor problems in monkeys are severe or fatal when the virus enters a human being. Over the eons that monkeys have developed, their diseases have developed with them. There are certain strategies that all diseases develop to survive. One is that to be spread successfully, they must not kill their natural host. But when they enter the wrong host species, the strategies that keep them in check do not work. The virus multiplies out of control and often attacks tissues and organs in ways it does not do when it is present in monkeys. The same, wrong-host phenomenon is why bird flu and equine encephalitis are dangerous to people but rarely kill birds and why the hanta viruses that causes no disease in rodent, kills humans.

What Kind Of Monkeys Are The Most Likely To Transmit Disease?

First generation and wild imported monkeys are most likely to carry diseases transmissible to man.

Monkeys that are from large groups are also more likely to harbor these diseases

Monkeys in poor health are also more likely to shed transmissible disease.

Monkeys housed under conditions of poor nutrition, mixed species, unsanitary environment, multiple caretakers, and high stress are also more likely to shed pathogens.

Monkeys species that are native to Africa and Asia are more of a health threat than monkey species that normally live in Central and South America.

Monkeys that are in traveling road shows, photo ops, carnivals and petting zoos, that do not have an adequate disease monitoring program are also more likely to put the public at risk.

What Are Some Of The Diseases That People Can Catch From Monkeys?

At this time, the two most dangerous diseases that people might catch from monkeys in the United States are tuberculosis and the herpes-B virus.

All monkeys need to be tested at least annually for tuberculosis and their caregivers need annual TB tests too. People with positive TB tests should never handle monkeys. Monkeys that mingle with the public, particularly Old World monkeys, should be tested three times a year. Even then, mingling monkeys with the public is an exceptionally foolish idea.

All Old World Monkeys should be tested for herpes-B when they are first obtained. They should only be obtained from breeders whose stock is confirmed to be free of herpes-B virus. They should be tested again if they are ever exposed to another monkey whose herpes-B status is unknowns or in doubt.

The following diseases are listed alphabetically - not on how frequently they affect humans or how serious they might be. For most, screening tests are available that will identify monkeys that carry the disease. Some can be eliminated from the monkey with medications, some can be prevented by vaccination , but many can not.

Amoebiasis

Monkeys are known to carry Entamoeba histolytica , the cause of amoebic dysentery in humans. However, there are other amoeba in monkeys that may not be dangerous to humans. The fact that a pet monkey is domestically bred is no guarantee it is free of amoeba. It is generally spread through direct fecal contamination and sewage. People working with carrier monkeys are at risk of contracting amoeba.

Pet monkeys need to be screened with a test for this intestinal parasite ( E. histolytica II test (Techlab)).

African Green Monkey Disease AKA Marburg Disease, African Hemorrhagic Virus Diseases, Vervet Monkey Disease

Despite the name, this is not primarily a disease of monkeys. These monkey hemorrhagic fevers are not something you will catch from a domestically born pet monkey When monkeys are exposed to this virus in their homelands, they die rapidly. It is probably really a disease of fruit bats.
Monkeys can ,however, harbor a similar virus – the Gamma-2 herpesvirus, that apparently causes them no harm. Great apes, including chimps and gibbons can carry a similar virus.

The virus that causes Green Monkey disease is a filovirus , a close relative of the Ebola virus. Flioviridae are among the most deadly organisms known to infect people.

One isolate of these virus in a shipment of green monkeys arriving in Marburg, Germany in 1967 from Uganda killed a number of scientists working with them. Beginning 3-9 days after exposure, the virus caused severe headache, rash, malaise, high fever, diarrhea and muscle pain. Patients that died, did so due to spontaneous haemorrhage. Seven out of the 25 workers who were infected died.

The CDC in Atlanta has the capability to test for this virus.

Campylobacter

Campylobacter are bacteria capable of causing severe diarrhea, fever, cramps and pain in people that usually lasts no more than a week . However, it occasionally becomes chronic and debilitating.

Some monkeys are chronic carriers of Campylobacter. Monkeys can be tested to see if they harbor these organisms with a PCR test or with an Rapid ELISA test

Ebola (Ebola-Reston)

Americans have a fascination with this virus due to a movie, Outbreak, that is very loosely patterned around the Ebola virus. However, the movie is pure fantasy. Monkeys are not long-term carriers of Ebola virus. When the CDC gave Ebola virus to monkeys, the virus was no longer present in the surviving monkeys in 19 days.
When monkeys catch this disease, they die as quickly as humans do - so pet monkeys could not harbor it. However, in Africa, dead monkeys are eaten – and eating the meat of monkeys that died in an Ebola outbreak will transfer the virus to humans. Like Marburg virus, fruit bats are probably the source of infection.

A second form of Ebola, the Reston Ebola Virus, was first found in crab-eating macaques (Cynomolgus Monkey) in Reston VA in 1989. It is fatal to monkeys but is non-lethal to humans.

Helicobacter pylori

Helicobacter pylori is a bacteria that lives in the stomach and intestine. It usually causes no symptoms, but it has been linked to indigestion, peptic ulcers and stomach cancer. How this bacteria spreads between humans is unknown. Most people who have it , did not catch it from monkeys, but we know it is present in rhesus and cynomologus monkeys in the United States.

Hepatitis A

Hepatitis A is a disease that can go either way - from monkey to man or from man to monkey. Monkeys that carry the hepatitis-A virus do not usually appear ill. It is present in monkeys in the United States
In some areas of the World many monkeys are carriers of this virus.
An ELISA test on the monkey’s blood will detect exposure to the virus, but it will not prove that the monkey is a carrier. Monkeys can be given the killed human Hepatitis-A vaccine to prevent the disease.

Hepatitis B

Hepatitis B is a more serious disease in humans than hepatitis A. This is because hepatitis B can lead to chronic liver damage. Monkeys, particularly great apes commonly carry the hepatitis B virus. Some of the strains of hepatitis B found in monkeys appear to be native monkey strains, while others appear to have been contracted from humans.
All monkeys should be screened for Hepatitis B. Antibody-based tests are most commonly run, but the PCR test for virus is the most reliable way to identify monkeys that are shedding this virus
Monkeys can be vaccinated against hepatitis B. if you vaccinate monkeys, look for a vaccine that is mercury-free or ref 2 or ref 3

Herpes B AKA B Virus, Cercopithecine herpesvirus 1, Herpesvirus simiae, Monkey B Virus)

Herpes B virus is a common problem in certain monkeys called macaques. In some studies, 73-100% of macaque monkey colonies harbor this virus.
Although it causes only a mild disease in these monkeys, it can be deadly to humans if they contract the virus. Although only 24 people were known to have contracted Herpes B from monkeys through 1992, 19 of those died. Herpes B is to monkeys much like Herpes Simplex (fever blisters) are to humans. In monkeys,
Herpes B causes ulcers and bubbles (vesicles) on the tongue and edges of the lip. Occasionally these ulcers form on the face or genitals. They clear up over 7-14 days but the virus does not leave their bodies. When the monkeys are later stressed, or for no apparent reason at all, they will shed the virus again in their saliva – this time it is often without oral symptoms.

Mother monkeys do not appear to spread this virus to their offspring before birth. In one survey, nearly 100% of captive macaques older than 2.5 years showed evidence of infection, while only 20% of those younger than 2.5 years did.

Herpes B virus usually transfers to humans through a bite or scratch or contamination with monkey saliva. In monkeys, it is also a sexually transmitted disease. In humans, the incubation period of the disease varies from 2 days to 5 weeks.

In my opinion, every breeder of macaque monkeys should be able to furnish a recent copy of a laboratory analysis that proves his animals are free of this virus. Because monkeys only shed the virus from time to time, two tests need to be run. The first the PCR test will detect monkeys that are actually shedding virus at the time of the test. For this test, an oral cotton swab (mucosal swab) needs to be provided. The second test, an antibody test, will tell which monkeys harbored the virus in the past and may shed virus again the future. For this test, a blood sample is necessary. If even a single monkey on the premises tests positive for either test, all should be treated the same as a carrier monkey. Negative test results for monkeys under one year of age can be unreliable.

If you are bitten or scratched by a macaque who’s B-virus status is unknown, the wound needs to be flushed and scrubbed for at least 15 minutes with povidone iodine or chlorhexidine solution. If none is available, then with antibacterial detergent soap. The same goes for a saliva contamination of the eye or a similar event although in this case, with sterile saline. Then a physician needs consult the CDC's Recommendations for Prevention of and Therapy for Exposure to B Virus (Cercopithecine Herpesvirus 1) .

Salmonella

Salmonella are bacteria that cause diarrhea in humans. Many kinds pets can infect humans with salmonella – including monkeys. Monkey stool specimens need to be screened for this bacteria. It is most dangerous to the very old, the very young and people in poor general health.

Shigella

Monkeys are a common source of shigelic dysentery in humans. Monkey stool specimens need to be screened for this bacteria. Like salmonella, it is most dangerous to the very old, the very young and people in poor general health. Most monkeys recover from their initial infection with shigella - but some continue to harbor the bacteria. It is occasionally fatal to monkeys if the do not receive adequate fluids to replace that lost through diarrhea.

Simian Foamy Virus

People who are exposed to monkeys are at risk of acquiring this virus.
To date, it has not been associated with any disease in humans. 70-90% of non-human primates born in captivity have SFV. The Canadian Health Agency has a summary of information on SFV. African and Asian monkeys seem to be the natural carriers .

Foamy virus have been reported in New World Monkeys as well. But it is unclear if these are the same virus present in African and Asian monkeys. A PCR Test for foamy virus is available - but it is used primarily to screen monkey tissues being used in human vaccine production.

Simian Immuno-deficiency viruses (SIV), T-cell leukemia virus, Mason-Pfizer Monkey Virus, And Other Retrovirus

Because Old World monkeys are used and examined so frequently in human AIDS research, a very large number of monkey retrovirus have been identified in them. These are retrovirus similar to human AIDS virus, but they are found naturally in at least 40 types of African monkeys. These virus have the potential to cause a disease in monkeys similar to AIDS in humans but many monkeys seem to carry the virus without any signs of illness. Macaques that are kept in close proximity to African monkeys can also become infected and ill or just become carriers. One of these retrovirus, causes leukemia in monkeys.
What these virus might do in humans is unknown.
These virus will infect people who work in close proximity to monkeys and are considered a potential health risk to humans.
I suggest that all Old World monkeys be screened for these virus.

Because positive mother macaques can pass it to their babies, the fact an Old World Monkey was born in the US is no guarantee it is free of SIV virus.

Strongyloides stercoralis

This intestinal parasite affects both humans and monkeys. It has been reported in Squirrel monkeys and Rhesus monkeys , but could probably be carried by any monkey.

It is a disease of poor sanitation; and sanitation is a great challenge when working with monkeys. In people, the parasite first causes rash and itching as it burrows through the skin. It then invades the lungs and eventually the intestines. The parasite is not eliminated by the most common worming medicines given to pet monkeys (pyrantel pamoate) however another medication , used in a continuing health maintenance program, will eliminate it.

Tuberculosis

Old World monkeys, are very susceptible to tuberculosis, 2nd ref .
New World monkeys are more resistant, but I know of outbreaks in squirrel monkeys, spider monkeys and owl monkeys. Other New World monkeys are susceptible to TB as well. 3rd ref.
There are many strains of TB. Monkeys are susceptible to all of them, but in the United States, infection with the human strain is most common. Certain wild populations of monkeys (baboons) seem more inclined to infection with the cattle strain (which also will infect humans).

Tuberculosis causes a different disease in monkeys than humans. In macaques, even the exposure to small numbers of TB organisms causes a rapid and fatal disease; whereas only 10% of people who are exposed develop any sickness and when they do, the disease is gradual and chronic.

The signs in monkeys are usually depression and weight loss and sometimes diarrhea – only a few monkeys with TB actually cough. But some monkeys do have the potential to become chronic carriers and spreaders. 1st ref and 2nd ref

Veterinarians cannot determine if pet monkeys carry TB through an office health examination. Identifying carrier monkeys requires a TB test, in which, a small amount of test solution (tuberculin) is injected into the skin of the monkey’s eyelid or chest.
Pet monkeys should have this test performed once (or , in certain instances, twice) a year.

The test, however, is not foolproof. Some monkeys with extensive TB give negative TB test results (anergy) . Also, the strength of tuberculin used to test varies by manufacturer. It is important that the tuberculin used be strong (1,500 units/0.1ml) – or a false-negative result can be obtained. Ref 2. The only currently available product I know of in the US that is satisfactory is Synbiotic's tuberculin OT (Product 97-8800).

If the TB status of a monkey is in doubt, A more sensitive test should be run that measures blood interferon-gamma The test requires only a blood sample, so it is much easier to run than the skin test. It is commercially available.

Occasionally, monkeys will test positive to tuberculosis due to their exposure to the bird form of TB (Avian tuberculosis). In humans , this strain of TB is usually -but not always less serious than the human and cow (bovine) strains. When it affects humans, it has the peculiar name of Lady Windermere syndrome.

What If I Have More Questions?

There are very few reliable sources of information on diseases transmissible to humans from pet monkeys. Monkeys are not common pets – so the experience of most veterinarians and public health officials is quite limited. Veterinarians with advanced knowledge in this area , generally work in governmental monkey colonies, pharmaceutical research facilities or zoos . They are generally quite reticent in dealing with the public. There are also big holes in our knowledge as to which disease organisms can or can’t be passed from monkeys to humans and disagreement as to whether these organisms are capable of causing disease in humans once they are passed.

Just bringing up the word “pet monkey” makes local and national public health authorities, such as those at the CDC, cringe. They tend to give blanket, simplistic answers and err on the side of extreme caution. You cannot blame them. The Special Pathogens Branch of the CDC, Atlanta, has the duty of dealing with organisms transmitted through monkeys. They will not talk to you about a specific exposure, but they might discuss a specific case with your physician. They will not give recommendations on preventative care for pet monkeys because they do not believe their should be any pet monkeys.

I still get involved in these cases from time to time. It is a frustrating and exhausting experience - dealing with and upset monkey owner fearful of loosing her beloved pet, an upset person who has been bitten and upset governmental officials – so I try to avoid it. Besides, there is often no good answer as to what should be done.

Can I Have My Monkey Tested For These Diseases?

Yes. I outlined the tests I suggest for various diseases in this article. Others can be found in the 2008 NIH Policy Manual .

Can I Have My Monkey Vaccinated To Prevent Some Of These Diseases?

Monkeys can be protected from some of these diseases, but no vaccines exist for others.

You can refer to the Simian Society website for some suggestions: No vaccines are FDA approved in the United States for use in monkeys. Using these products is what is called an "off label' use. Before giving vaccines to monkeys that were not intended for use in monkeys you must be certain that the organisms in the product are completely killed or that veterinarians and monkey owners have found that the products are safe and effective for use in monkeys. This information passes through word-of-mouth because the off-label use of vaccines exposes veterinarians to liability and legal issues.